2015 Volume 11 Issue 3 Pages 246-256
Objective. Potential environmental impacts related to water has drawn much attention in recent year. The rapid increase of interests leads to the publication of the international standard（ISO14046）on water footprint at August, 2014. Many impact assessment methods applicable to water footprinting have been developed. However, the targets and characteristics of existing methods are various due to the diversity of potential environmental impacts related to water. In addition, impact assessment in water footprinting（water footprint impact assessment）can be classified into four types（water scarcity footprint, water availability footprint, water footprints addressing water degradation, water footprint profile）, which may confuse practitioners to choose appropriate methods for each type of assessment in application studies. Thus, currently developed methods applicable to water footprint impact assessment are reviewed and characterised according to the types of water footprint impact assessment.
Results and Discussion. Water scarcity footprint and water availability footprint assess the potential impacts in terms of physical scarcity of water resources compared with water demand. At midpoint level, basic concept to indicate the impacts by the ratio of water demand and available resource amounts is common to all corresponding methods. However, differences in formulation of indicators, spatial resolution and temporal resolution can be found. Especially in water availability footprint, two methods are applicable but require more efforts for practitioners to collect information on quality of water resources. At endpoint level, methods for assessing impacts on human health, ecosystem and resources can be applicable. On the other hand, the target impacts even at same endpoint are different from method to method. Wide range of characters including the units of indicators can be figured out. Regarding water footprints addressing degradation, while existing impact assessment methods on categories related to water pollution by chemical substances are applicable, target areas of them are mostly region/country specific. Grey water can be an option as a proxy to express the stress of water pollution although it does not necessarily indicate the potential impacts that actually happen. Global scale assessment models will be expected to be developed concerning on thermal pollution that has not been dealt in conventional life cycle impact assessment. Water footprint profile can be achieved by summarising some or all results of other three methods on water footprint impact assessment. While some methods propose to integrate the results on different aspects into single index, weighting and its results shall be compliant with ISO14044.
Conclusions. While there are differences among existing methods for water footprint impact assessment, summarised characters of each method in this paper corresponding to each type of water footprint impact assessment will be useful for practitioners to make a decision on the selection of methods according to their scope of the assessment. Unified and consensual method and indicators are more desirable for the sake of avoiding confusion in practice. The activities in WULCA working group are expected to achieve the goal in future. From the viewpoint of methodology development, harmonization of inventory databases and impact assessment methods is necessary for more precise assessment at detailed spatial and temporal resolution.
